Summary

This contribution emphasizes the significant rock-building role of microbial encrusting organisms includingTubiphytes, filamentous cyanobacteria (mainlyGirvanella andOrtonella), andArchaeolithoporella in the Carboniferous to Permian buildups that formed on seamounts in the Panthalassa ocean. The description concentrates on the paleontological characters of these microbes and the petrographic properties of the microbial bindstones and related cryptomicrobial fabrics. Comparisons of major rock-building biotas in the Carboniferous-Permian Panthalassan buildups and Pangean reefs are briefly discussed.

The Lower Carboniferous (Visean) to upper Middle Permian (Murgabian) limestone units and the upper Lower to upper Middle Permian (Artinskian to Murgabian) limestone units in southwest Japan were examined. All these limestone units are underlain by oceanic island-type basalts and are totally free from terrigenous materials. The limestones are lying in disrupted accretionary terranes of Japan and are regarded as relicts of oceanic buildups upon seamounts in the Panthalassan open-ocean realm.

Thin-section studies revealed that the sediment-binding and stabilizing of filamentous cyanobacteria,Tubiphytes, andArchaeolithoporella contributed significantly to the formation of several varieties of microbial bindstone and related cryptomicrobial fabrics. Sessile foraminifers,Girvanella and related filamentous cyanobacteria formed bindstones and cryptomicrobial micritic laminae/mats in which skeletal debris and peloidal grains have been trapped. Minute shrubs ofOrtonella and related filamentous cyanobacteria acted as small-scale sediment-bafflers as well as sediment-binders.Tubiphytes bindstone was formed by the low-laminar and dense insitu growth ofT. obscurus, often encrusted by filamentous cyanobacteria.T. sosioensis formed complicated bodies that are completely encrusted byArchaeolithoporella and cemented by syndepositional carbonate cement.

These microbial bindstones and related cryptomicrobial fabrics are present in almost all the stratigraphic levels, especially in Upper Carboniferous and Permian carbonate sections. In contrast, boundstones, characterized by large-sized, wave-resistant frameworks and built by rugose corals, chaetetids, and bryozoans, only occurring in laterally discrete patches, dominate in an interval ranging from the Upper Visean to the Lower Moscovian. The microbialites and filamentous cyanobacteria-related cryptomicrobial fabrics, though less conspicuous and much smaller-sized, dominanted on the Panthalassan oceanic buildups during Carboniferous to Permian time when most large-sized frame-builders were globally impoverished.

The Visean to early Moscovian abundance of the coralchaetetid-bryozoan association in the examined Panthalassan buildups is of special importance for the discussion on the recovery of the reef ecosystem after the end-Devonian crisis. The Panthalassan buildups differ from their time-equivalent Pangean reefs in the ability to construct wave-resistant reefs. These wave-resistant coral-chaetetid-bryozoan reefs were replaced by the post-Moscovian microbial carbonates, which characterize the Upper Carboniferous and Permian development of the carbonate buildups of the Akiyoshi and Mino teranes. A modification of the ‘Akoyoshi reef model’ is proposed.